I read many questions regarding using an existing nextcloud for using as e-os-backend. (for example: Use Nextcloud instead of ecloud
I don’t know if I got it right- I understood, e-os-cloud is based on nextcloud with some additions.
It is possible to use an existing nextcloud for syncing addresses, calendaers, notes, etc.
But can I backup my photos this way?
If it should work, I just can tell, in my case it doesn’t. maybe it doesn’t work because my nextcloud installation has an url with a subdirectory: https://my-nextcloud-address.domain/nextcloud/
Am I right that this is the reason for the non-working backup of photos?
Not necessarily. /e/'s sync functionality, particularly the photos sync, has a number of outstanding issues and is not very reliable, even using /e/'s own cloud. Best solution is to disable /e/'s document and photo sync in /e/'s, install the NextCloud sync client app, and use that for photo and documents sync.